1. Field of the Disclosure
Embodiments disclosed herein relate generally to centrifuges for the separation of a suspension with one or more liquid phases of different specific gravities. In another aspect, embodiments disclosed herein relate to centrifuges convertible between two-phase and three-phase operations. In a more specific aspect, embodiments disclosed herein relate to centrifuges convertible between two-phase and three-phase operations via use of a changeable weir insert, where the conversion may be performed without dismantling the centrifuge.
2. Background
Centrifuges are often used to effect separation of liquid-solid mixtures. For example, well drill cuttings, drilling mud, slop oil, and other wastes generated during drilling of wells and general chemical processing may be separated using a centrifuge. Such mixtures may include solids and one or more of oleaginous fluids and aqueous fluids.
When used to separate three-phase mixtures, such as an oil/water/solids mixture, typical centrifuges allow for the separation of the solid from the fluids, i.e., two-phase separations. The fluids are subsequently separated using additional equipment. Other centrifuges are specifically designed for three-phase separation, allowing for separate recovery of the oil and the water phases.
The liquid-solid mixtures encountered for a given process or for a desired use of a centrifuge may vary, and may include two-phase mixtures, three-phase mixtures, and the oil to water ratio may additionally vary from low, mostly water, to high, mostly oil. Centrifuges that may be configured to allow for separation of either two-phase or three-phase mixtures are described in, for example, GB 1569520A and U.S. Pat. No. 4,615,690 (‘the '690 patent). Additionally, mention of centrifuge modification to transform a centrifuge from three-phase operation to two-phase operation is mentioned in EP 181953 A1.
GB 1569520A describes a centrifuge apparatus allowing for conversion between two-phase operation and three-phase operation. For two-phase operation where only one liquid phase is to be removed, all the openings to the receiving chamber which houses the skimmer mechanism are opened, while the radially-directed outlet openings are closed. A weir-barrier has been removed so that only the skimmer mechanism operates and draws off the liquid phase. For three-phase operation, i.e., if two liquid phases of different specific gravity must be removed separately, a portion of the openings are closed at their ends away from the separation chamber in the axial direction, and the outlet passages for these openings are opened. The weir-barrier is installed in such a way that the openings (connected as before with the receiving chamber which houses the skimmer mechanism) are connected with the separation chamber in a radially outward region, thus collecting the liquid phase of higher specific gravity while the other openings, with the aid of the weir-barrier, are connected with the separation chamber in an inner radial region, and thus collect the liquid phase of lower specific gravity, which is then conducted through associated outlet passages into a collector.
Similarly, U.S. Pat. No. 4,615,690 ('690) discloses a centrifuge apparatus allowing for conversion between two-phase and three-phase operation, where FIG. 1 illustrates such a centrifuge (a reproduction of FIG. 1 of the '690 patent). If all the openings 4 remain open to the receiving chamber 5, the decanter is in two-phase operation, i.e., the suspension introduced into the separation chamber 2 is separated into a solid phase and liquid phase, the whole of the latter of which is withdrawn through the skimmer mechanism 7, as described in greater detail in GB 1569520A. In three-phase operations, i.e., separation of a suspension into a solid phase, to be carried out by the screw conveyer, not shown, and two liquid phases of different specific gravities, indicated in FIG. 1 by the different liquid levels in the separation chamber, with the heavier liquid phase occupying the radially outward space of the pool, the two liquid phases are to be drawn off separately. The respective levels of the two liquid phases are determined by the skimmer disks or weirs 11. A first subset of the openings 4 are closed at their ends toward the separation chamber by covers 10, and thus separated from the receiving chamber 5, while the remaining subset of the openings 4 are opened at that same end, and thus communicate with the receiving chamber 5.
Varying such centrifuges from two-phase operation to three-phase operation can be cumbersome and time consuming. For example, it may be required to remove the entire cover flange, shaft, and other portions of the centrifuge to effect the change from two-phase to three-phase operations. Such operations may require transport of the centrifuge, or at least a portion thereof, to a machine shop for change of the operating configuration in a controlled environment.
U.S. Pat. No. 3,968,929 discloses a centrifuge in which the liquid level in the centrifuge may be controlled by replacing inserts without dismantling of additional components of the centrifuge. No teaching is provided with respect to conversion between two and three phase operations, and skimmers and other components necessary for three-phase operation are each internal to the centrifuge.
Other patents disclosing use of weir discs, each internal to the centrifuge, include U.S. Pat. Nos. 3,955,756, 5,885,202, 6,030,332, and 7,115,202, among others.
Accordingly, there exists a need for centrifuges that are easily converted from two-phase to three-phase operation and vice versa.